1. Field of the Invention
The present invention relates to a camera having a two lens group zoom system composed of a front lens group and a rear lens group and, more particularly, to an apparatus and method for controlling motors for driving the lens groups.
2. Related Background Art
A recent demand is to reduce the outer dimensions of camera, particularly of compact camera. Especially, an important subject is to miniaturize a lens barrel as much as possible. To miniaturize the lens barrel, a recent trend in camera having the two lens group zoom system is to replace a mechanical cam system with a mechanism for driving the front lens group and the rear lens group by separate motors.
In such a motor driven mechanism, a direct current motor is employed as the motor for driving the front lens group and a stepping motor as the motor for driving the rear lens group. Also, a drive method of the motors is generally the so-called simultaneous drive method in which the stepping motor is driven in several pulses during continuous drive of the direct current motor.
The simultaneous drive method of the front and rear lens group driving motors could have, however, an error operation of the motors, if the battery is exhausted so as to lower the drive voltage for motors. In particular, in case of the stepping motor, a rotational shaft could not be rotated, when a drive voltage is below a certain value. Since a position of rear lens group is detected from the total number of pulses output from CPU to the stepping motor, a failure in drive of stepping motor would result in a deviation between an actual position and the position of rear lens group obtained from the pulse number. This so-called step-out state is an especially significant problem to be solved, because recent cameras tend to employ a smaller battery with lower voltage, specifically changing from 6 V type to 3 V type, with a decrease in size of camera.
Consequently, a need exists for a way to accurately locate the front lens group and the rear lens group at desired positions even with a decrease in drive voltage.